1. Field of the Invention
The present invention relates mainly to a printing apparatus composed as a thermal transfer type using a thermal head.
2. Description of the Related Art
Recently is a mounting demand for an apparatus for reproducing the displays of CRTS and other display screens in color hard copies. As it is easily maintainable, an apparatus for thermal transfer on paper using a color ink sheet having yellow, magenta and cyan colors has been particularly in demand.
For this type of printing apparatus, various structures have been hitherto proposed, and in a general structure, each printing paper separated from the paper supply unit is conveyed along the conveying path into the printing unit where the platen roller and thermal head are opposite to each other, and the printing paper positioned, that is a predetermined leader portion of the printing paper is detected and aligned and the printing processing is executed with respect to the printing paper while being conveyed, and is discharged to the paper discharge unit.
In the case of color printing, the printing paper is moved reciprocally plural times between the platen roller and thermal head by changing the color of ink sheet every time.
This type of printing apparatus is conventionally known in the structures as shown in FIG. 1 to FIG. 4.
FIG. 1 is, for example, a sectional view of a conventional printing apparatus disclosed in the Japanese Patent Application Laid-Open No. 63-249674 (1988). In the drawing, numeral 1 denotes a paper supply unit, 5 is a pinch roller and 10 is a discharge roller. The printing paper P supplied from the paper supply unit 1 is wound around the platen roller 6 by about a half circumference pinch rollers 5, 5 and platen roller 6, and laid over the ink sheet S stored in an ink sheet cassette 8, and while moving the printing paper P and ink sheet S, thermal transfer is effected by the thermal head 7, and the paper is discharged through the discharge roller 10.
In color printing, on one same printing paper P, portions of ink sheet S of plural colors are laid down sequentially to reproduce a color copy. In this case, after printing of one color, the platen roller 6 rotates in the reverse direction of printing operation to return the printing paper P to the print start position, and a different color from the first is printed on the same position of the printing paper P. This operation is repeated as many time as necessary, and when printing is over, the printing paper P is discharged out of the apparatus from the discharge roller 10 through the platen roller 6.
In the conventional printing apparatus shown in FIG. 1, meanwhile, the platen roller 6 has a large diameter, and the paper supply unit 1 and paper discharge unit 2 are located at both sides of the platen roller 6, and separately in the upper and lower directions from the platen roller 6, and therefore the size of the printing apparatus is large, and since the printing paper P is wound around the platen roller 6 and becomes curly, which gives rise to troubles in conveyance. Color deviation is also likely to occur in color printing with such a system.
To solve the problem of the large size of the above described printing apparatus, other printing apparatus were proposed, for example, as shown in FIG. 2 and FIG. 3.
FIG. 2 is, for example, a schematic side view of a conventional printing apparatus disclosed in the Japanese Patent Application Laid-Open No. 180839 (1987). In this printing apparatus, at one side of the platen roller 6 constructing the printing unit 3, a paper supply unit 1 and a paper discharge unit 2 are disposed, and the platen roller 6 is provided with a clamper 6a. In the conveying path from the paper supply unit 1 to the platen roller 6, conveying rollers 9, 9 and stationary paper guides Ga, Ga are disposed, while in the conveying path from the platen roller 6 to the discharge roller 10, there are movable paper guide Gg and stationary paper guide Gb.
As shown in FIG. 2(a), the printing paper P is individually supplied by the paper supply roller 1a from the paper supply unit 1 and is provided to the conveying roller 9. The paper is then conveyed to the opposing position of the thermal head 7 and platen roller 6 while being regulated by the stationary paper guide Ga, and with the front end portion thereof being clamped by the clamper 6a of the platen roller 6, it is taken up on the platen roller 6 along with the rotation of the platen roller 6. The thermal head 7 is lowered onto the platen roller 6 together with the ink sheet S, and is pressed against the surface of the printing paper P, so that thermal transfer is effected by the thermal head 7.
When printing is over, the platen roller 6 stops, and the thermal head 7 retracts. The movable paper guide Gg descends to abut against the circumference of the platen roller 6, thereby changing the conveying path to the discharge roller 10 side.
Finally, as shown in FIG. 2(b), the platen roller 6 rotates in the reverse direction to that of the printing operation, and the printing paper P is sent out to the discharge roller 10 side along the movable paper guide Gg and stationary paper guide Gb, and is discharged out of the apparatus by the discharge roller 10.
On the other hand, FIG. 3 is, for example, a side view disclosed in the Japanese Patent Application Laid-Open No. 63-286761 (1988). In this printing apparatus, similarly, the paper supply unit 1 and paper discharge unit 2 are disposed in the upper and lower positions at one side of the printing unit 3, and the printing paper P is supplied individually from the paper supply unit 1 through the paper supply belt 1b is wound up on the circumference of the pinch roller 5 from the lower side of the platen roller 6, and is laid over on the ink sheet S on the platen roller 6, to perform thermal transfer by the thermal head 7. When printing is over, the movable paper guide Gg slides on the circumference of the platen roller 6, so as to discharge the printing paper P into the paper discharge unit 2 through the paper supply belt 1b.
During color printing in such a device, the printing paper P is rotated as many times as necessary along the circumference of the platen roller 6 so as to contact with ink sheets S of different colors to print these different colors. Symbol F denotes a cooling fan of the thermal head 7.
In the conventional printing apparatus shown in FIG. 2 and FIG. 3, since the paper supply unit 1 and paper discharge unit 2 are disposed in upper and lower positions at one side of the printing unit 3, the size can be notably reduced. However, since the diameter of the platen roller 6 is large, and downsizing is limited, and since in the structure of printing by winding the printing paper P on the platen roller 6, being same as in the printing apparatus shown in FIG. 1, the printing paper P is likely to be curly, and the number of parts increases because the conveying path for suppling the printing paper P and the conveying path for discharging are changed by operation of the movable paper guide Gg, and since the movable paper guide Gg is located near the platen roller 6, it is difficult to remove the paper in the event of paper jamming.
As the means for solving the problems in the conventional printing apparatus shown in FIG. 2 and FIG. 3, the printing apparatus as in FIG. 4 is known.
In FIG. 4, the paper supply unit and paper discharge unit (neither shown) are disposed at one side (the left side in FIG. 4) of the printing unit 3, and the platen roller 6 is made small in diameter, and capstan roller 4 and pinch roller 5 are disposed opposedly across the conveying path immediately before the platen roller 6, that is, at the side of paper supply unit 1 and paper discharge unit 2, and the conveying path connecting the capstan roller 4 and platen roller 6 are formed nearly in a linear form.
In such a conventional printing apparatus, although the size is further reduced by reducing the diameter of the platen roller 6, it is necessary to determine the entire layout about the conveying path of the printing paper P, including the relation with the paper supply unit 1, paper discharge unit 2, and printing unit 3, but this point has not been considered sufficiently.
Incidentally, the paper supply unit 1, paper discharge unit 2 and printing unit 3 which is composed of the thermal head 7 and ink sheet cassette 8 and others in the conventional printing apparatus are structured as described below.
FIG. 5 is a schematic side view showing a practical construction of the paper supply unit 1 in the conventional apparatus, and FIG. 6 is a perspective view of essential parts seen from the bottom side of the same, in which numeral 11 denotes a paper cassette for composing the paper supply unit 1. The paper cassette 11 comprises a casing 12 and a core member 13, and the casing 12 is open at the front side and in the front side bottom in the paper supply direction of the printing paper P, and a top plate 12a is disposed in the upper portion, and the core member 13 is provided inside. Below the paper cassette 11, a paper supply roller 14 and a push-up member 15 are disposed, and a stationary paper guide 16 is installed further ahead.
The core member 13 has separation pawls 13b, 13b for supporting the lower portion of the right and left corners at the front end side of the supplying direction of the printing paper P stored in the casing 12, and the right and left side walls of the rear end portion are pivoted on the side wall of the casing 12 by using a shaft 13c. The push-up member 15 and arm 14a of the paper feed roller 14 are coaxially pivoted by using a shaft 15a, and they are rotated in the direction of arrow around the shaft 15a by a drive unit not shown, while the paper supply roller 14 is rotated, and the push-up member 15 contacts with or departs from the contact piece 13d of the core member 13, and the paper supply roller 14, with or from the bottom of the printing paper P exposed in the lower side of the casing 12. As a result, the paper feed roller 14 is rotated about the shaft 15a, and contacts with the lower side of the printing paper P with a predetermined pressure, and by the frictional force acting between them, the printing paper P at the lowest position is separated from the others, and is fed forward.
The operation of such paper supply unit 1 is explained below by reference to the explanatory view of FIG. 7.
FIG. 7 shows the paper supply state, in which the push-up member 15 is rotated about the shaft 15a and abuts against the contact piece 13d, and pushes and rotates the core member 13 until the upper surface of the printing paper P abuts against the top plate 12a about the shaft 13c, with the both sides of the front portion of the printing paper P held in the separation pawl 13b, and stops in the state being thrust upward.
The arm 14a is also rotated in the same direction, and presses the paper supply roller 14, which is rotated and driven, to contact with the lower side of the printing paper P with a predetermined pressure. By the frictional force acting between the paper supply roller 14 and printing paper P, the printing paper P at the lowest position is separated from the other printing papers, and the front end portion slips out of the separation pawl 13b, and is guided by the stationary paper guide 16 to be fed into the printing unit 3.
The paper supplying position of the printing paper P is moved from position D to position E as the number of sheets decreases.
In such a conventional paper supply unit 1, meanwhile, since the paper supplying position moves from D to E depending on the number of sheets of the printing paper P, when the storage capacity of the printing paper P is increased, the interval of the stationary paper guides 16 is also increased accordingly, and the stationary paper guides 16 come to occupy a wide space.
FIG. 8 is, for example, a schematic plan view showing the positioning means of printing paper P for the printing unit 3 in the conventional printing apparatus disclosed in the Japanese Patent Application Laid-Open No. 1-290465 (1989), and FIG. 9 is its schematic side view. At one side of the opposing positions of platen roller 6 and thermal head 7, that is, at the opposite side of the layout position of the capstan roller 4 and pinch roller 5, stationary paper guides 17a, 17b are disposed opposedly above and beneath, and a conveying path for switchback is formed. The front end of the upper stationary paper guide 17a serves also as the guide of the ink sheet cassette 8, and a hole Gc is provided in the center of the rear end portion, and a front end sensor SE is disposed here, and a reflector 18 is disposed in the opposing lower stationary paper guide 17b. When the printing paper P is detected by the front end sensor SE, the rotation of the capstan roller 4 is stopped, and the printing paper P is positioned, that is, predetermined leader portion is detected and aligned.
The operation of such positioning means is described below by reference to the explanatory view shown in FIG. 10. When supplying paper, as shown in FIG. 9, the thermal head 7 is waiting aside above the platen roller 6, and the printing paper P is conveyed in the arrow direction by the pinch roller 5 and capstan roller 4, and is led in between the stationary paper guides 17a, 17b. When the front end of the printing paper P comes to the sensing point of the front end sensor SE, driving of the capstan roller 4 stops, thereby finishing the detection and alignment of the printing paper P.
As shown in FIG. 10, the thermal head 7 descends until the ink sheet S contacts tightly with the printing paper P, and the platen roller 6 and capstan roller 4 are rotated and driven reversely, and the printing paper P is switched back in the arrow direction, and the thermal head 7 is heated to make printing.
In color printing, after printing one color in the step shown in FIG. 10, the printing paper P is switched back and returned to the position shown in FIG. 9, and the ink sheet S of the next color is detected, and thereafter the operation shown in FIG. 9 and FIG. 10 is repeated as many times as required.
In such conventional positioning means, in the case where the beginning of the printing paper P is detected, since the distance between the front end sensor SE of the printing paper P and the heat generation unit 7a of the thermal head 7 is long, the printing paper P sags on the way, and slipping occurs between the printing paper P and capstan roller 4, pinch roller 5, and the printing paper P may run obliquely, and the positioning precision is poor, the print start position is likely to be dislocated, and color deviation occurs in color printing.
FIG. 11 is, for example, a schematic plan view showing a thermal head and its positioning means in a conventional printing apparatus disclosed in the Japanese Patent Application Laid-Open No. 63-132065 (1988), and FIG. 12 is its schematic side view. The thermal head 7 is shaped like a rod, comprising a linear heating portion 7a in the middle of the lower side opposite to the platen roller 6, and radiation fin 7b in the upper side, and the middle portion of the holding members 21, 21 disposed at both ends in the longitudinal direction is pivoted in the middle of the support arms 22a, 22a of the pressing member 22 through the shafts 21a, 21a.
The pressing member 22 has a pressing plate 22b opposing to the thermal head 7 in a straddling manner over the upper sides of the front end portions of support arms 22a, 22a in an L-shape in side view, and plural contact springs 23 are disposed between the pressing plate 22b and the upper surface of the thermal head 7, accumulating a dilating force, and each base end portion is pivoted on the shaft 22c, and drooping pieces 22d disposed at both ends of the front end portion of the support arms 22a, 22a are provided with notches 22a to be engaged with the shaft 6b of the platen roller 6, while stopper pieces 22f, 22f are projected at the positions confronting the rear end portions 21c of the support members 21, 21.
The operation of such thermal head 7 is explained referring to the explanatory view of FIG. 13.
FIG. 13(a) shows a state of the thermal head 7 in the waiting position, and in this state, by the dilating force of the contact spring 23, the holding member 21 and support arm 22a of pressing member 22 are thrust in the mutually departing directions, and the rear end portion 21c of the holding member 21 is abutting against the stopper piece 22f.
When pressing the thermal head 7 to the platen roller 6, by the drive unit not shown, the pressing member 22 is rotated in the arrow direction shown in FIG. 13(b) about the shaft 22c together with the holding member 21, and the thermal head 7 abuts against the circumference of the platen roller 6, and the notches 22g formed in the support arm 22a of the pressing member 22 are engaged with the shaft 6b of the platen roller 6, thereby relatively positioning the thermal head 7 and platen roller 6.
From the state in FIG. 13(b), when the pressing member 22 is further rotated, since the thermal head 7 is contacting with the platen roller 6, the contact spring 23 is compressed, and the thermal head 7 is pressed by the platen roller 6 to be in the state shown in FIG. 12, thereby pressing the thermal head 7 to the platen roller 6 and positioning the heating portion 7a of the thermal head, and in this state the heating unit 7a is heated to make printing.
In such conventional thermal head 7 and its holding member 21, looseness is likely to occur between the notch 22g and shaft 6b for relatively positioning the thermal head 7 and platen roller 6, and color deviation occurs, but, to &lt;the contrary, when the fitting of the notch 22g and shaft 6b is too tightly, the contact pressure of the heating portion 7a in the thermal head 7 changes, and uneven density occurs, and the load of the platen roller 6 on the shaft 6b increases to cause driving loss, and the rotating speed of the platen roller 6 varies, and color deviation occurs similarly.
FIG. 14 is, for example, a schematic plan view showing driving unit and cooling means of a thermal head 7 in a conventional printing apparatus disclosed in the Japanese Utility Model Application Laid-Open No. 63-37243 (1988), and FIG. 15 is its schematic side view, in which another shaft 24 is disposed parallel to a shaft 22h for pivoting the base end portion of a support arm 22a at the pressing member 22, the shaft 24 being provided with cam 24a and gear 24b to slide and contact with the shaft 22h and this gear 24b is coupled with a motor M1 through reduction gear 24c and worm gear 24d.
As the cooling means of the thermal head 7, a radiation fin 7b is disposed on the upper surface of the thermal head 7, and a cooling fan 25 is installed above the thermal head 7. The radiation fin 7b is dense in the interval thereof in the middle of the longitudinal direction corresponding to the distribution of the accumulated heat temperature of the thermal head 7 shown in FIG. 16, and loose in the interval thereof gradually as going toward the both ends therefrom, so as to cool corresponding to the accumulated heat distribution of the thermal head 7.
The cooling fan 25 is installed so as to blow air always down toward the thermal head 7 side as indicated by arrow shown in FIG. 15. Numeral 26 is a stopper, disposed at the upper side of the both end portions of the thermal head 7, and is linked to the support arm 22a of the pressing member 22, thereby regulating the mutual maximum spacing distance.
The other parts are identified with the same reference numbers as the corresponding parts in the conventional apparatus shown in FIG. 11 and FIG. 12.
The operation of the thermal head 7 is explained below by reference to the explanatory view shown in FIG. 17. FIG. 17(a) shows the waiting state, in which air is blown to the thermal head 7 by the cooling fan 25.
When pressing the thermal head 7 to the platen roller 6, first the motor M1 shown in FIG. 15 is rotated to turn the shaft 24 and drive the cam 24a, and the pressing member 22 and the thermal head 7 are rotated together in the direction of the arrow in broken line as shown in FIG. 17(a), then the thermal head 7 is fitted to the circumference of the platen roller 6 as shown in FIG. 15.
From the state shown in FIG. 15, the cam 24a is further rotated, and the contact spring 23 is compressed by the pressing member 22, and the thermal head 7 is pressed against the platen roller 6 as shown in FIG. 17(b) to make printing. At this time, the heat from the thermal head 7 is released through the radiation fin 7b, while air is brown in from the cooling fan 25 to cool.
The cooling means, incidentally, may comprises a cooling fan F as shown in FIG. 3.
In such conventional cooling means, the surface area of the radiation fin 7b is small, and a sufficient cooling effect is not obtained for the amount of heat generated by the thermal head 7, and since the cooling fan 25 or F is installed above the thermal head 7, even while the thermal head 7 is at waiting position, the position of installation of the cooling fan 25 or F is high in order to avoid mutual interference, and to the contrary, the distance from the thermal head 7 is long while printing, resulting in the cooling effect being smaller, and moreover the overall height of the printing apparatus becoming high, and when the heat is accumulated more in the thermal head 7, the ink of the ink sheet S sublimes in excess, and is transferred on the printing paper P, and hence the printing density varies with the passing of the time.
FIG. 18 is, for example, a perspective view of an ink sheet cassette 8 in a conventional printing apparatus disclosed in the Japanese Patent Application Laid-Open No. 63-47179 (1988). The ink sheet cassette 8 comprises a cylindrical feed side bobbin 31 winding an unused ink sheet S, and a cylindrical takeup side bobbin 32 for taking up the used ink sheet S, which are incorporated inside thereof in parallel to each other with each one end exposed outside.
Such ink sheet cassette 8 is stored in a storage magazine 33, and is inserted into or removed from the printing apparatus in a state of coupling the bobbins 31, 32 with a reel device 34. The reel device 34 is designed to take up the ink sheet S by rotating the bobbin 32 about its axial center line by means of a drive unit not shown.
In such conventional ink sheet cassette 8, when detaching or attaching it, the storage magazine 33 must be drawn out to the front panel of the printing apparatus by sliding in the arrow direction, and the ink sheet cassette 8 is taken out by putting a hand into the storage magazine 33, and the ink sheet cassette 8 must be put in, and it takes time to detach and attach the ink sheet cassette 8, and the slide mechanism is needed for inserting the storage magazine 33 into the printing apparatus or removing it therefrom, and the number of parts of the printing apparatus increases on the whole.
FIG. 19 is, for example, a perspective view of a drive system corresponding to the reel device 34 (see FIG. 18) and discharge roller 10 (see FIG. 1 and FIG. 2) in a conventional printing apparatus disclosed in the Japanese Patent Application No. 63-122572 (1988). In the drawing, numeral 41 is a gear linking with a reel device 34, and 42 is a gear linking with a discharge roller 10 of printing paper P. The both gears 41, 42 are disposed by keeping their axial center lines parallel and deviating by a predetermined interval in the axial center line direction, and in the middle of the both gears 41, 42 is disposed a shaft 44 of a square section formed integrally with the shaft of a worm wheel 43, and a relay gear 45 is put on the shaft 44 so as to slide thereon through a compression spring 44a.
On the side of the relay gear 45, that is, on the opposite side of the contact side of the compression spring 44a, one fork-shaped end of a changeover lever 46 having the middle portion pivoted by a shaft 46a is located opposedly across the shaft 44. At the other end of this changeover lever 46, an engaging groove 46b is provided, and this engaging groove 46b is engaged with a pin 47a projecting a little close to the peripheral side of the worm wheel 47. The worm wheels 43, 47 are linked with respective motors M2, M3 through worm gears 48, 49.
Such drive system is explained below by reference to the explanatory views of operation shown in FIG. 20 and FIG. 21. FIG. 20 shows the engaged state of the relay gear 45 and gear 41 linked with the reel device 34 of the ink sheet cassette 8, while the relay gear 45 and the gear 42 linked with the discharge roller 10 are not engaged.
The driving force of the motor M2 is transmitted only to the gear 41 through worm gear 48, worm wheel 43, shaft 44 and relay gear 45, and the reel device 34 is driven. Next, when the motor M3 rotates in a predetermined direction, the worm gear 49 and worm wheel 47 rotate, and the changeover lever 46 rotates about the shaft 46a through a pin 47a, and the relay gear 45 oscillates in the arrow direction against the dilating force of the compression spring 44a, so that the relay gear 45 is released from the gear 41 and is engaged with the gear 42 as shown in FIG. 21.
In this state, the driving force of the-motor M2 is transmitted only to the gear 42, and the discharge roller 10 is driven, and the reel device 34 stops. When the motor M3 rotates in the reverse direction, the relay gear 45 is released from the gear 42, and is engaged with the gear 41 to return to the state shown in FIG. 20.
Thus, in the conventional drive system as abovementioned, the motor M3 is necessary separately for changing over the transmission of driving force, and the number of motors increases, resulting in the mechanism being complicated, the reliability being lowered, and the entire apparatus becoming larger in size.